(481f) Towards Predictive Modeling of Crystallization Fouling: Taking into Account Fouling Layer Structures

Towards Predictive Modeling of
Crystallization Fouling: Taking into Account Fouling Layer Structures

Jie Xiao, Feng Zhang, Jian Han, Xiao Dong Chen

Suzhou Key Laboratory of Green Chemical
Engineering

School of Chemical and Environmental
Engineering

College of Chemistry, Chemical Engineering
and Materials Science

Soochow University, Suzhou, Jiangsu
Province 215123, China

Abstract

The fouling
layers formed on heat exchanger surfaces exhibit complicated structures, which
essentially determine flow hydrodynamics, fouling kinetics and hence the heat transfer
performance. In-depth
understanding of deposit layer formation and its structural effects on the
fouling process could lead to effective fouling mitigation or even prevention
strategies. The exploration tasks, however, are not trivial due to a lack of
knowledge of the crystallization process and the complicated deposit structure.

In
this talk, I will summarize our past and on-going efforts on numerical simulation
of different stages of a complex crystallization fouling process, focusing on
deposit layer growth and its impact on the fouling process.  The developed
method incorporates a pseudo-dynamic scheme where the dynamic fouling process
is approximated as a set of sequential steady-state processes taken place in a
continuously varying geometric domain. This unique approach allows the
characterization of mass, momentum and heat conservations of a continuous flow of
liquid over a growing fouling layer. Dynamic evolution of the fouling layer surface
and its intricate interactions with hydrodynamics and fouling kinetics can then
be rigorously taken into account. The introduced model was validated using the experimental
data for a calcium sulphate fouling system. The effects of the solution chemistry
and operating conditions on fouling resistance evolution were quantified
through a comprehensive parametric study.  Furthermore, we are developing methods that can be used to quantitatively evaluate the
effects of fouling layers' interior structures on fouling dynamics. We
have systematically investigated four representative schemes for fouling layer
characterization: i.e., a homogeneous porous medium that is impermeable to
water (HoIm), a heterogeneous porous medium that is impermeable to water
(HeIm), a homogeneous porous medium that is permeable to water (HoPe), and a
heterogeneous porous medium that is permeable to water (HePe).  Under the
same operational conditions, four models offer significantly different
prediction results on the fluid velocity, temperature distribution and fouling
resistance. It can be concluded that numerical model development should take
the fouling layer structure into account, and the scheme of HePe that best
resembles a real fouling layer structure should be a promising option.

Keywords: Crystallization fouling; fouling
inhibition; fouling layer structure; CFD model; pseudo-dynamic scheme